Fort Collins, CO Invasive Plant Rules: Prohibited Species (2026)

Chapter 20, Article IV, Weeds, Brush Piles and Rubbish, defines Weed in § 20-41 as an aggressive, non-native herbaceous plant detrimental to native plant communities or agricultural lands, followed by a named list that includes jointed goatgrass, quackgrass, redroot pigweed, common and giant ragweed, wild oat, white, wild and black mustard, whitetop, sandbur, diffuse, spotted and Russian knapweed, Canada thistle, bindweed, leafy spurge, St. Johnswort, kochia, prickly lettuce, perennial pepperweed, dalmatian and yellow toadflax, purple loosestrife, buckhorn plantain, curly dock, Russian thistle, horsenettle, black nightshade, buffalobur, perennial sow thistle, Johnsongrass, dandelion, fanweed, puncturevine, cocklebur, and marijuana, plus any other type of noxious weeds designated by the Colorado Weed Law or Larimer County Weed District.

Unlike the ordinary grass-height rule, which caps unmowed grass at nine inches under § 20-42(c)-(d), the noxious-weed prohibition in § 20-42(h) applies regardless of height, meaning even a single stem of a listed species is a violation the moment it appears, not just when it grows tall. The rule folds in the state and county noxious-weed lists by reference, so species the Colorado Department of Agriculture or the Larimer County Weed District later designates are automatically covered without a City ordinance amendment. Code Compliance can issue a notice of violation and order removal under § 20-44, with unpaid removal costs assessed as a lien against the property, similar to the height and rubbish violations elsewhere in the Article.